No it wasnt your immagination. CO express flies the 145XR (extended range) and as said before they are the sole operator of them. For some reason though, CO did not paint these winglets, however they are just grey. Hope this helped.

Winglets are added to reduce the size of wingtip vortices, which cause drag, therefore increasing fuel efficiency which in turn extends range. Also because drag is reduced take off and climb performance generally increases. The lasted added benefit is also usually increase cruise performance. But mind you this increase is usually only a few percentage points which pays off over time. However you need to literally weigh the increase of adding the winglets to adding the weight to the airplane.